Method of grease manufacture



March 22, 1966 Q Dom JR, ET AL 3,242,086

METHOD OF GREASE MANUFACTURE Filed May 22, 1963 United States Patent 3,242,086 METHOD OF GREASE MANUFACTURE Clarence L. Dowden, Jr., and William R. Coons, Jr., Port Arthur, and William -R. Hencke, Groves, Tex., as-

signors to Texaco Inc., New York, N.Y., a corporation of Delaware Filed May 22, 1963, Ser. No. 282,336 8 Claims. (Cl. 25241) This invention relates to an improved method for the manufacture of lithium hydroxy fatty acid soap thickened greases. It relates particularly to an improved method for preparing lithium hydroxy fatty acid soap thickened greases of the rheopectic type.

In accordance with this invention, lithium hydroxy fatty acid soap thickened greases are prepared by a low temperature method wherein the saponificat'ion is carried out at a temperature in the range from about 180 F. to about 200 F. with continuous shearing of the saponification mixture. The shearing is preferably accomplished by recirculating the saponification mixture at a relatively rapid rate from a maintained body thereof through a recycle line containing a shearing means, which is suitably a shear valve set to give a substantial pressure drop across the valve. Recirculation of the grease mixture without shearing is very advantageously carried out following the saponification and throughout the remainder of the process.

We have found that shearing during the saponification step in the above manner produces greases of superior smoothness which undergo a large amount of hardening upon milling, differently from the effect of shearing during later stages of the heating cycle which produces a large amount of hardening of both the milled and unmilled product. By carrying out the process with shearing during the saponification and milling in the conventional manner during the finishing step, greases of excellent texture and appearance are obtained in yields which are substantially higher than those obtained by milling products obtained by the low temperature processes of the prior art. This method is employed with special advantage in the preparation of greases which are difiicult to prepare in satisfactorily smooth form, such as greases comprising highly paraflinic oils thickened with above about 5 percent by weight of a lithium hydroxy fatty acid soap obtained by the saponification of a hydroxy fatty acid glyceride.

Greases of the so-called rheopectic type, which undergo a large amount of hardening upon shearing, are obtained by the process of this invention carried out with shearing during the saponification as described above and without any substantial amount of additional shearing in later stages of the heating cycle. The method of this invention is specially adapted to produce fluid grease containing about 2-9 percent of lithium hydroxy fatty acid soaps which form N.L.G.l. No. 02 grade greases upon only moderate shearing, such as that obtained by milling with one pass through a colloid mill at 0.003 inch clearance or that to which the grease is subjected in an automotive bearing.

In accordance with the preferred embodiment of our invention, the grease mixture is recirculated continuously during both the heating and cooling cycles and additional oil at a lower temperature is introduced into the recycle stream during the cooling process, as described by L. F. Badgett, W. R. Hencke and F. T. Crookshank in their copending application Serial No. 282,330, filed of even date herewith. The process is carried out very advantageously by introducing additional oil at a higher temperature than the grease mixture into the recycle stream during heating up to the maximum temperature. By carrying out the process in this manner, the above advantages together with greatly reduced manufacturing times are obtained.

The figure is a diagrammatic illustration of one form of apparatus suitable for making greases in accordance with the preferred embodiment of this invention.

Referring in more detail to the figure, numeral 1 represents a jacketed grease kettle equipped with stirrer 2 and adapted to be heated to elevated temperatures above about 350 F. In carrying out the grease preparation, the grease kettle is charged with saponifiable material, lubricating oil and lithium hydroxide, very suitably in the form of the monohydrate, in approximately the stoichiometric amount required to react with the saponifiable material. If desired, a small excess of lithium hydroxide may be employed, such as to give a grease containing up to about 0.5 percent of free lithium hydroxide. Water is preferably employed in the reaction mixture in a weight ratio with the lithium hydroxide monohydrate of at least about 5:1, respectively, and usually at least about 6:1, respectively, although smaller amounts may be employed in some cases, down to amounts in a weight ratio with the lithium hydroxide monohydrate of about 1:1. The lubricating oil and saponifiable material are employed in a weight ratio from about 2:1 to about 10: 1, respectively, and preferably from about 4:1 to about 7:1, respectively.

The kettle contents are heated with stirring up to the maximum temperature employed, which ordinarily requires about 1-5 hours, including a holding period in the range from about 180 F. to about 200 F. for at least a suflicient time to substantially complete the saponification reaction with recirculation and shearing as described below.

Recirculation of the kettle contents is begun when the mixture has been heated to about 180 F. or during the heating up to this temperature if desired, and carried out continuously during the heating in the range from about 180 F. to about 200 F. at a rate such that the weight of recycled saponification mixture equals the total weight of saponification mixture, i.e., one batch turnover, in from about 0.1 minute to about 15 minutes, preferably in from about 0.25 to about 10 minutes, and ordinarily in from about 0.25 to about 5 minutes. The mixture is heated within this temperature range for a period from about /2 hour to about 2 hours, until at least 5, and preferably at least about 10 batch turnovers have been obtained. Recirculation of the grease mixture is begun by turning valves 6 and 8 to the open position and starting pump 12. The grease mixture passes through line 5,

heating and cooling to the recirculating stream of grease mixture. The shear valve is suitably a gate valve, set in a partly closed position so as to give a pressure drop of about 20-200 pounds per square inch, and preferably about 2-5l25 pounds per square inch across the valve. When the process is carried out to produce rheopectic greases, pump 12 is preferably a pump of a type wherein the fluid is subjected to only a relatively small amount of shearing, suitably a positive displacement rotary type pump wherein the grease mixture is sheared at a rate below about 10,000 reciprocal seconds, and preferably at a rate below about 5,000 reciprocal seconds.

Recirculation of the grease mixture through the recycle line may be begun immediately after charging the grease kettle if desired, and carried out continuously throughout the grease making process. When the process is carried out to produce fluid rheopectic greases, the recirculation is preferably carried out following the saponification step with shear valve 19 in the wide open position. When greases of the conventional type are being prepared, shearing of the grease mixture during a portion or all of the additional heating cycle and during the cooling cycle may be employed if desired.

Circulation of the grease mixture through the recycle system during the heating cycle following the saponification step is carried out at a rate sufiicient to give one batch turnover within about 22 minutes, such as in about 0.322 minutes, and preferably in about 0.415 minutes, based on the weight of grease mixture during the heating cycle, or in about 0.25-10 minutes, and preferably 0.312 minutes, based on the average weight of grease mixture during the heating cycle when the process is carried out with additional oil added during the heating step as described hereinbelow. Recycling during the cooling cycle is suitably carried out at a rate sutficient to provide a batch turnover in about 0.535 minutes, and preferably in about 1-20 minutes, based on the weight of the finished grease, or in about 0.4-27 minutes, and preferably about O.5-l7 minutes, based on the average weight of grease mixture during the cooling cycle.

Very advantageously, the recycling is carried out for a minimum period of about 15 minutes, and preferably for at least about 30 minutes, during the heating cycle following the saponification, until at least batch turnovers and preferably at least 10 batch turnovers, based on the average weight of the grease mixture during this period, are obtained. The recycling is preferably carried out continuously throughout the heating cycle following the saponification step.

The maximum temperature to which the grease mixture is heated is ordinarily in the range from above about 300 F. to just below the melting point of the soap, preferably at least about 10 F. below the melting point of the soap. In the preparation of lithium 12-hydroxystearate thickened greases, the grease mixture is preferably heated to a top temperature in the range from about 310 F. to about 375 F. The grease mixture is ordinarily heated within this temperature range for a period of at least about 15 minutes, such as from about 15 minutes to 1 hour, although longer heating periods in this temperature range may be employed if desired.

Cooling of the grease mixture is carried out by cutting off the heat to the kettle, and to the recycle line if such additional heating is employed, and introducing lubricating oil from tank into the recirculating stream of grease mixture. The added oil is at a temperature substantially below that of the grease mixture, such as at least about 100 F., and preferably at least about 150 F., below the temperature of the grease mixture at the beginning of the cooling step. The lubricating oil passes from tank 20 into line 36 by way of line 22 containing valve 23, pump 24, line 25 and line 26 containing valve 27, dial thermometer 33, pressure gauge 34 and valve 35. Valve 35 is preferably a one way valve, most suitably of a type designed to prevent gravity flow of oil through pump 24 when the pump is not operating, such as a diaphragm controlled reducing valve or a spring loaded check valve. In line 36, the oil may pass into the recirculating stream of grease mixture at the intake of pump 12 by passing through valve 37 into line 10, or into the grease mixture at the discharge side of pump 12 by passing through valve 38 into line 14. It is preferably passed into the grease mixture at the intake side of pump 12, particularly when valve 19 is operated in the wide open position, in order to obtain increased mixing and shearing by the action of the pump. The oil may be introduced into the recirculating stream of grease mixture at a rate such that the ratio of the rate of flow of grease mixture before the point of confluence to the rate of oil injection is from about 1:1 to about 400:1, preferably in a ratio from about 2:1 to about 150:1, and most advantageously in a ratio from about 3:1 to about 50.21, by weight, respectively.

The oil addition is preferably commenced at the beginning of the cooling step, and may be carried out over the entire cooling period or during only a portion thereof. Additional cooling may be applied to the kettle, and also to the recirculating stream of grease mixture. The amount of lubricating oil added during the cooling may amount to from about 10 to as high as about 90 percent of the total oil contained in the grease. It will usually be from about 25 to about 75 percent of the total oil contained in the grease. When the oil addition is carried out during only a portion of the cooling step, it is advantageous in some cases to continue recirculation of the grease mixture down to the drawing temperature. The cooled grease mixture is finally drawn through line 40 containing valve 41.

In the grease preparation carried out by the method comprising a particularly preferred embodiment of this invention, the saponification is carried out in the presence advantageously, the saponification may be carried out in the presence of lubricating oil in a weight ratio from about 4:1 to about 6: 1, respectively, with the saponifiable material, and additional oil added in this manner sufficient to give an oil-soap ratio at top temperature from about 6.5 :1 to about 12:1, respectively. The preheated oil is introduced into the recycle line by passing from tank 20 to heater 30 by way of line 22, pump 24, line 25 and line 28 containing valve 29. Heater 30 may be any suitable type of heater, such as a coil heater, as indicated in the diagram. From heater 30 the oil passes into line 26 and is introduced into the circulating stream of grease mixture at either the intake or the discharge side of pump 12 as described hereinabove in connection with the introduction of the oil during cooling. The temperature of the oil added in this manner is preferably substantially higher than that of the grease mixture, and may be up to or even slightly higher than the melting point of the soap. The rate at which this oil is introduced may suitably be such that the ratio of the rate of recirculation of the grease mixture to the rate of oil injection is Within the ranges disclosed hereinabove in connection with the introduction of cold oil during the cooling cycle. The amount of oil added in this manner may be from about 5 percent up to about 50 percent of the total oil employed in the grease. It is ordinarily from about 10 to about 30 percent of the total oil contained in the finished grease.

Greases of the conventional type prepared by the above process may be finished with milling in the usual manner. However, when the process is carried out with recycle shearing of the grease mixture in later stages of the process following the saponification step, greases of the desired consistency may be obtained directly without milling. Milling is not employed in the preparation of rheopectic greases.

The greases which are prepared in accordance with this invention comprise a lubricating oil as the chief component and a minor amount, sufficient to thicken the lubricating oil to a grease consistency, of a lithium soap of a fatty acid material comprising .at least about 35 percent by weight of a hydroxy fatty acid material. Preferably the soap comprises at least a major proportion, and most suitably at least about 75 percent by weight, of a lithium hydroxy fatty acid soap. The amount of lithium soap will ordinarily vary from about 2 percent by weight up to about 20 percent by weight of the composition, although somewhat smaller or larger amounts of soap may be employed in some cases.

Suitable soap-forming hydroxy fatty acid materials which may be employed in the production of these greases are essentially saturated hydroxy fatty acids containing 12 or more carbon atoms and one or more hydroxyl groups separated from the carboxyl group by at least one carbon atom, and the glycerides and lower alkyl esters of such acids. The acid preferably contains about 16 to 22 carbon atoms per molecule. Such materials may be obtained from naturally occurring glycerides produced synthetically by methods such as the hydroxylation of fatty acids or the hydrogenation of ricinoleic acid or castor oil. Particularly suitable materials of this character are 12-hydroxystearic acid and the .methyl ester thereof and hydrogenated castor oil. 'Such hydroxy fatty acid materials may be employed in the saponification in admixture with saponifiable materials of the conventional type, as disclosed, for example, by H. V. Ashburn and O. P. Puryear in US. 2,450,220. The preferred saponifiab'le materials of the latter type are saturated fatty acids containing from about 16 to 24 carbon atoms per molecule and the glycerides of such acids The lubricating oils employed in these greases include particularly the conventional mineral lubricating oils having Saybolt Universal viscosities in the range from 'about'70 seconds at 100 F. to about 225 seconds at 210 F., and synthetic hydrocarbon oils having viscosities in this range, such as those obtained by cracking and polymerizing products of the Fischer Tropschprocess and the like. The mineral lubricating oils may be'naphthenic or 'parafiinic oils or blends of different oils of these types. Other synthetic oleaginous compounds such as polyesters, polyethe-rs, etc., having viscosities within the lubricating oil viscosity range may also be employed in these greases as at least a part of the lubricating oil component. Suitable compounds of this type include particularly the aliphatic dicarboxylic acid diesters, such as, for example, di-Z-ethylhexyl sebacate, di(secondary amyl) sebacate, di-Z-ethylhexyl azelate, di-iso-octyl adipate, etc. However, a lubricating oil which is substantially unreactive under the saponification conditions is preferably employed in the saponification mixture, mineral lubricating oils being particularly suitable for this purpose.

Various additives of the usual types, such as corrosion inhibitors, oxidation inhibitors, extreme pressure agents, anti-wear agents, etc. maybe employed in these greases. Suitable oxidation inhibitors include particularly those of the amine type, such as diphenylamine, phenylalphanaphthylamine and tetramethyl diatmino diphenyl methane, etc. Very advantageously, the greases may contain from about 3 to 12 percent-by weightof a sulfurized fatty oil, such as sufurized sperm oil containing about 5-15 percent by weight of sulfur, and about 13 percent by weight of a lead soap, such as lead naphthenate. Lead naphthenates obtained from relatively low molecular weight naphthenic acids, such as those having molecular Weights in about the range from about 120 to 235, and preferably in the range from about 200 to about 230, are particularly suitable for this purpose. By means of this additive combination, high extreme pressure properties are imparted to rheopectic lithium hydroxy fatty acid soap thickened greases prepared by the method of this invention without any substantial impairment of their rheopectic properties.

The following example is illustrative of grease preparations carried out by the preferred method of this invention.

EXAMPLE I A rheopectic lithium 12-hydroxystearate grease was prepared in the manner described below.

The equipment employed in the preparation of this grease was a pound capacity steamheated laboratory kettle with auxiliary equipment for grease circulation with shearing and with hot and cold oil injection into the recycle stream as shown in FIG. 1. The circulation equip ment consisted of a 1% inch pipe connecting the kettle drawotf with a model H124SViking Pump connected with a variable drive giving a pump capacity of about 2-10 gallons per minute, and a inch pipe extending from the pump to the top of the kettle, containing a gate valve employed as a shear valve.

The following materials were employed in this preparation: The lubricating oils employed were a deasphalted and steam refined paraflinic residual oil from a mixed base crude having a Saybolt Universal viscosity of about 159 seconds at 210 F. and an APll gravity of 21.4 degrees, and a paraffinic distillate oil having a Saybolt Universal viscosity at 100 F. of about 184 seconds and an API gravity of 29.6 degrees. The saponifiable material employed was a commercial hydrogenated castor oil having a saponification number of about 179, an acid value of about 1.5, an iodine number of 3 and a titer of 74 C.

Following is a detailed description of the method employed in the grease preparation: The grease kettle was charged with 1.22 pounds oflithium hydroxide and 7.32 pounds of water, the mixture stirred until the lumps had dissolved, and 27.9 pounds .of the residual oil, 15.1 pounds of the distillate oil and 8.6 pounds of the hydrogenated castor oil added. Steam was then turned unto the kettle jacket and the recycle line jacket, and circulation of-the kettle contents through the recycle line was started at a rate of 2 gallons per minute with the shear valve in the wide open position. When the kettle contents had been heated to 180 F. the shear valve in the recycle line was set to give a pressure drop of 60 pounds per square inch across the valve. The kettle contents were maintained for one hour at a temperature in the range from 180 F. to 202 F. withcontinued stirring and recycling through the shear valve. The shear valve was then turned to the wide open position, and the grease mixture heated to 220 F. The injection of a mixture of 14 pounds of the residual oil and 7.5 pounds of the distillateoil, preheated to 350 E, into the recirculating stream of grease mixture at the intake side ofthe pump was: then begun at a rate of about 1.5 pounds per minute with full steam on the kettle and recirculation line, which resulted in raising the temperature of the grease mixtureto 255 F. in about 20 minutes. The grease mixture was then further heated up to 320 F. and held at 320-325 F. for 1 hour. The heating was then discontinued and the cooling carried out by circulating cooling water through the kettle jacket and the circulation line jacket, and by injecting a mixture of 23.7 pounds of the residual oil and 12.7 pounds of the distillate oil at ambient temperature into the recirculating stream of grease mixture at the intake side of the pump at a rate of about 1.5 pounds per minute until the grease mixture had been cooled to 260 F. When the grease mixture was cooled to 230 F 0.6 pound of diphenylamine, 1.68 pounds of lead :naphthenate and 8.4 pounds of sulfurized fatty oil were added. The total manufacturing time was 4 hours and 50 minutes.

A fluid product was obtained as described above. Upon milling with one pass through a Premier Colloid Mill set at 0.003 inch clearance, this product became an N.L.G.I. No. 2 grade grease of excellent texture and appearance.

The following table shows the effect of shearing during the holding period at ISO-200 F. in the preparation of the above grease. The greases of the table were of the same composition and prepared with recycling in the same manner during both the heating and cooling cycles and by otherwise substantially identical procedures except for the dilference in shearing as shown in the table.

Table I ASTM Penetration Grease No Shearing Appear Unrnillcd Milled ance (Milled) Un- Worked Un- Worked worked worked 1 None Rugl1 TS TS 257 284 2 From 230 F. on heating do 356 292 236 259 cycle to 200 F. on cooling cycle. 3 All;1 180-200 F. only, for 1 Smooth.-. TS TS 253 280 our.

1 Too soft for penetration test.

As shown by the above table, a rough textured grease of otherwise excellent rheopectic properties was obtained by the circulation procedure without shearing. By carrying out the process by the method of our invention with recycle shearing for one hour at 180200 F., a smooth product was obtained without any substantial effect upon its rheopectic properties. Circulation shearing at later stages of the process resulted in higher yields but destroyed the rheopectic properties, and the product obtained with shearing only at later stages of the process was less smooth than that obtained by shearing at 180-200" F.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In the preparation of lithium soap thickened greases by the process comprising saponifying a saponifiable fatty acid material comprising at least about 35 percent by weight of a hydroxy fatty acid material with a lithium base in the presence of at least a portion of the lubricating oil contained in the grease, heating at a higher temperature below the melting point of the soap to dehydrate, and finally cooling and adding any additional lubricating oil required to provide a grease of the desired grade, the improvement which comprises carrying out the saponification step at a temperature in about the range 180200 F. with continuous recirculation of the saponification mixture from a maintained body thereof through a recycle line containing a shear valve with a pressure drop of about -200 pounds per square inch gauge across the valve, said saponification mixture being recirculated at a rate such that the weight of recirculated saponification mixture is equal to the total weight of saponification mixture in about 01-15 minutes.

2. The process of claim 1 wherein the said saponification is maintained at a temperature in about the range ISO-200 F. for about 0.5-2 hours.

3. The process of claim 1 wherein the grease is finished by milling.

4. The process of claim 1 wherein the said recirculation is carried out at a rate such that the weight of recirculated grease mixture equals the total weight of grease mixture in about 0.25-5 minutes.

5. The process of claim 1 wherein the said saponifiable material is hydrogenated castor oil.

6. The process of claim 1 wherein the saponification is carried out in the presence of lubricating oil in an amount equal to from about 4 to 6 times the weight of the said saponifiable material and additional lubricating oil, preheated to a temperature above that of the grease mixture, is added following the dehydration in an amount sufficient to provide a mixture wherein the oil-soap ratio is from about 6.5:1 to about 12:1, respectively.

7. The process of claim 1 wherein the said recirculation is continued during further heating of the grease mixture obtained by the saponification and during the cooling step, without a pressure drop across the said shear valve.

8. The process of claim 1 wherein the said lubricating oil added during the cooling is injected into the circulating stream of grease mixture.

References Cited by the Examiner UNITED STATES PATENTS 2,332,202 10/1943 Calkins 25242.1 2,830,022 4/1958 Nelson et a1. 2524l 3,068,175 12/1962 Roach et al 252-39 3,079,341 2/1963 Coons et al 252--41 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner. 

1. IN THE PREPARATION OFLITYIUM SOAP THICKENED GREASES BY THE PROCESS COMPRISING SAPONIFYING A SAPONIDIABLE FATTY ACID MATERIAL COMPRISING AT LEAST ABOUT 35 PERCENT BY WEIGHT OF A HYDROXY FATTY ACID MATERIAL WITH A LITHIUM BASE IN THE PRESENCE OF AT LEAST A PORTION OF THE LUBRICATING OIL CONTAINED IN THE GREASE HEATING AT A HIGHER TEMPERATURE BELOW THE MELTING POINT OF THE SOAP TO DEHYDRATE, AND FINALLY COOLING AND ADDING ANY ADDITIONAL LUBRICATING OIL REQUIRED TO PROVIDE A GREASE OF THE DESIRED GRADE, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE SAPONIFICATION STEP AT A TEMPERATURE IN ABOUT THE RANGE 180-200*F. WITH CONTINUOUS RECIRCULATION OF THE SAPONIFICACTION MIXTURE FROM A M AINTAINED BODY THEREOF THROUGH A RECYCLE LINE CONTAINING A SHEAR VALUE WITH A PRESSURE DROP OF ABOUT 20-200 POUNDS PER SQUARE INCH GAUGE ACROSS THE VALVE, SAID SAPONIFICATION MIXTURE BEING RECIRCULATED AT A RATE SUCH THAT THE WEIGHT OF RECIRCULATED SAPONIFICATION MIXTURE IS EQUAL TO THE TOTAL WEIGHT OF SAPONIFICATION MIXTURE IN ABOUT 0.1-15 MINUTES. 